Purified hydrogen is used in the manufacture of many products including metals, edible fats and oils, and semiconductors and microelectronics. Purified hydrogen is also an important fuel source for many energy conversion devices. For example, many fuel cells use purified hydrogen and an oxidant to produce an electrical potential. A series of interconnected fuel cells is referred to as a fuel cell stack, and this stack may be referred to as a fuel cell system when combined with sources of oxidant and hydrogen gas. Various processes and devices may be used to produce the hydrogen gas that is consumed by the fuel cells.
As used herein, a fuel processor is a device that produces hydrogen gas from a feed stream that includes one or more feedstocks. Examples of fuel processors include steam and autothermal reformers, in which the feed stream contains water and a carbon-containing feedstock, such as an alcohol or a hydrocarbon, and partial oxidation and pyrolysis reactors, in which the feed stream is a carbon-containing feedstock. Fuel processors typically operate at elevated temperatures. Because the reforming and other fuel processing reactions are overall endothermic, the heat required to heat the fuel processors needs to be provided by a heating assembly, such as a burner, electrical heater or the like. When burners are used to heat the fuel processor, the burners typically utilize a combustible fuel stream, such as a combustible gas or a combustible liquid.
One such hydrogen-producing fuel processor is a steam reformer, in which hydrogen gas is produced from a feed stream that includes a carbon-containing feedstock and water. Steam reforming is performed at elevated temperatures and pressures, and therefore steam reformers typically include a heating assembly that provides heat for the steam reforming reaction, such as to maintain the reforming catalyst bed at a selected reforming temperature and to vaporize the feed stream. One type of heating assembly is a burner, in which a combustible fuel stream is combusted with air. Steam reformers conventionally utilize a feed stream that is vaporized and reformed to produce a mixed gas stream containing hydrogen gas and other gases, and a fuel stream that has a different composition that the feed stream and which is delivered to, and consumed by, the burner or other heating assembly to heat the steam reformer.